Method of making ferrite cores



Nov. 5, 1963 P. M. MILLER 3,109,817

METHOD OF MAKING FERRITE CORES Filed May 22, 1957 MAKE A MIXTURE OF THE FOLLOWING MATERIAL m POWDERED FORM MOLAR Mg0- --.----e.5 TO 2|.0

MnO --ae.0 r0 50.0 Fe O --s9.0 TO 43.0 zno --UI= T0 13.0

ADD BINDER WHICH DECOMPOSES INTO GASES WHEN HEATED PRESS-MOLD MIXTURE TO A BRIQUETTE 0F DESIRED SHAPE PLACE BRIQUETTE IN A FURNACE, HEATING IT GRADUALLY IN AIR TO 2,350 DEGREES FAHRENHEIT IIOO DEGREES, MAINTAINING SAID TEMPERATURE FOR SEVERAL HOURS, DURING WHICH A CONTROLLED AMOUNT OF NITROGEN IS INTRODUCED TO DISPLACE AIR, AND COOLING THE BRIQUETTE WHILE STILL IN THE FURNACE, IN THE PRESENCE OF PURE NITROGEN.

INVENTOR PAUL M. MILLER y C HIS ATTORNEYS United States Patent 3,109,817 METHGD OF MAKING FERRETE CGRES Paul M. Miller, Dayton, Ohio, assignor to The National Cash Register Company, Dayton, Shio, a corporation of Maryland Filed May 22, 1957, Ser. No. 650,892 8 Ciairns. (Cl. 25262.5)

This invention relates to magnetic-ferrite material and to a method of making it, said material having substantially square hysteresis loop magnetic characteristics, low coercivity, high remanence, and high resistance to change in polarity when repeatedly disturbed by low-level driving currents which individually are less than that required to change the polarity completely.

The ferrite material made by the novel method, from molded and sintered powdered metal oxides, is particular- 1y suitable for making magnetic core storage devices, of toroid shape, for electronic calculating machines, which storage devices can be driven by high-speed switching transistors. The ferrite material, further, is stable in the driving current requirements and output characteristics over a wide temperature range, such range being approximately between 50 degrees Fahrenheit and 125 degrees Fahrenheit.

The method is unique in that, in sintering, the heating and the cooling are carried on in a single step without removal from the furnace, the temperature being gradually elevated in an air atmosphere to the sintering temperature and held there for a number of hours preferably while nitrogen is added to the air, such nitrogen addition increasing the coercivity of the end product, to dilute or replace the air. After the sintering is completed, the ferrite material is allowed to cool in the furnace in the presence of nitrogen.

With these and other objects in view, which will become apparent in the specification and claims to follow, the invention will be described with reference to the drawing, which is a block diagram of the novel method.

The preferred form of the invention will be described with reference to the making of a transistor-driven toroidshaped magnetic-ferrite core. First, the desired mixture of metallic oxides, taken from the ranges shown in box 20 of the drawing, are pulverized to pass through a screen which will screen out particles over 180 microns in diameter. Second, a small amount of binder is added, so that the mixture can be press-molded into a briquette of the desired shape. And, third, the briquette is placed in a controlled-gas furnace for sintering, the briquette being heated in air until a temperature of 2,350 degrees Fahrenheit -100 degrees is reached, at which time the air is either diluted or replaced with nitrogen while the temperature is maintained at 2,350 degrees Fahrenheit i100 degrees for from three to ten hours, after which pure nitrogen is introduced to displace the air, if any is present, and the furnace is allowed to cool in the presence of nitrogen.

Following are specific examples of procedures in the making of a toroid core which, when finished, will have an outside diameter of 0.0801002 of an inch, an internal diameter of 0.0541002 of an inch, and a thickness of approximately 0.025 of an inch:

Example I. A mixture of the following ingredients in powdered form is made:

Molar percent MgO (as MgCO 14.25 MnO (as MnCO 40.82 Fe O 41.23 ZnO 3.70

This mixture is calcined in air at approximately 1,800 degrees Fahrenheit for approximately ten hours; during which the MgCO is converted to MgO and the MnCO is 'ice converted to MnO. The calcined mixture, which has begun to become ferritic, is pulverized and screened, so that the maximum particle size is about 180 microns in diam eter. To this pulverized mixture is added 1 percent, by weight, of polyvinyl alcohol, added as a 4 percent aqueous solution, said polyvinyl alcohol being so selected that thesolution has a viscosity of 4 to 6 centipoises as determined by the Hoeppler falling ball-method. The resultant tacky mass is granulated and thoroughly dried. Using particles of the granulated mass that are bet-ween and microns in diameter, 0.0055 gram is put into a press mold and briquetted into a toroid having an outside diameter of 0.096 of an inch, an inside diameter of 0.064 of an inch, and a height of 0.028 of an inch. This green toroid briquette is then heated in a furnace, in the pres ence of air only, to a sintering temperature of 2,350 degrees Fahrenheit 1100 degrees, where it is held for two hours. At the end of two hours, the air is replaced with nitrogen and the temperature maintained for four more hours. Thereafter, the furnace is cooled to room temperature, the now-sintered cores being kept in a nitrogen environment. The cores will have shrunk to the dimensions before specified for the (finished cores.

Example II. Using the green" briquette of Example I, the sintering temperature is maintained for two hours in air, followed by alternating the air with nitrogen every fifteen minutes for four additional hours at sintering temperature, followed by cooling in pure nitrogen.

Example Ill, using the green briquette of Example I, a mixture of two parts of nitrogen to one part of air is used for the six-hour sintering period, followed by cooling in nitrogen.

Example IV, using the green briquet-te of Example I, a gas mixture of equal parts of air and nitrogen is used during the six-hour sintering period.

The foregoing examples provide cores that have high output currents when switched by relatively low input currents. To get variations which may be desirable for certain applications, the sintering time may be varied, good results being obtained in the range of from three to ten hours, and the mixture of metallic oxides may be varied within the ranges set forth in box 20 of the drawing.

The novel features of the method are, first, the use of all or part nitrogen in the sintering temperature period, followed by cooling in nitrogen; and, second, that the heating, the sintering, and the cooling are done in a single continuous operation without removal of the treated material from the furnace.

Qther materials than polyvinyl alcohol may be used as binders in proper solutions, among which are slightly hydrolyzed starches, emulsified poly-glycols, methyl-cellulose, and other similar organic materials.

What is claimed is:

1. The method of making magnetic-ferrite material including the steps of molding a briquette of a mixture of pulverized magnesium oxide, manganese oxide, iron oxide, and zinc oxide within the ranges shown in the drawing; heating the briquette in a furnace, first in air to 2,350 degrees Fahrenheit i100 degrees; controlling the furnace to maintain said temperature for from three to ten hours and during this time introducing a selected amount of nitrogen into the furnace to replace an equivalent amount or" air according to increased coercivity desired in said magnetic-ferrite material; and cooling the sintered briquette in the furnace in nitrogen.

2. The method of claim 1 in which a small amount of binder, that decomposes into gases upon being heated, is used to hold the briquette together until the briquette is consolidated by the heating process.

3. The method of making a magnetic-ferrite core including the steps of molding a toroid-shaped briquctte from pulverized magnesium oxide, manganese oxide, iron oxide, and zinc oxide in desired amounts within the ranges shown in the drawing; heating the briquette in a controlled-gas furnace up to 2,350 degrees Fahrenheit 1-100 degrees in air; maintaining the temperature of the briquette, While still in the furnace, at 2,350 degrees Fahrenheit 1-100 degrees for a period of from three to ten hours; introducing into the furnace at selected amount of nitrogen during the three-to ten-hour period according to increased coercivity desired in said magnetic-ferrite core; and finally cooling the briquette in the furnace in nitrogen.

4. The method of treating a briquetted mixture of magnetic-ferrite-producing metal oxides selected from the ranges shown in the drawing to produce magnetic-ferrite objects, consisting of a continuous heating and cooling operation while the briquette remains in a controlled-gas furnace, said ope-ration being characterized by introducing air into the furnace while the briquette is heated up to 2,350 degrees Fahrenheit i100 degrees; maintaining the temperature in the furnace at 2,350 degrees Fahrenheit 1-100 degrees for from three to ten hours, during which time a selected amount of nitrogen is introduced into the Molar percent MgO 14.25 MnO 40.82

F8203 ZnO 3.70

using as a binder a 4 percent aqueous solution of polyvinyl alcohol, said solution having a viscosity of 4 to 6 oentipoises as measured by the Hoeppler falling ball method, and the amount of polyvinyl alcohol amounting to about 1 percent, by Weight, of the mixture; placing the briquette in a controlled-gas furnace and raising the temperature to a sintering temperature of 2,350 degrees Fahrenheit :100 degrees in air; maintaining the sintering temperature for six hours, the air being displaced by nitrogen during the last four of the six hours; and cooling the "briquette in nitrogen without removal from the furnace.

6. The method of making a magnetic-ferrite toroid core including the steps of pressing into a toroid briquette 0.0055 gram of a pulverized mixture of Molar percent MgO 14.25 MnO 40.82,

FC203 ZnO 3.70

using as a binder a 4 percent aqueous solution of polyvinyl alcohol, said solution having a viscosity of 4 to 6 centipoise as measured by the Hoeppler falling ball method, and the amount of polyvinyl alcohol amounting to about 1 percent, by Weight, of the mixture; placing the briquette in a controlled-gas furnace and raising the temperature to a sintering temperature of 2,350 degrees Fahrenheit :100

Molar percent MgO 14.25 MnO 40.82 F8 0 41.23 ZnO 3.70

using as a binder a 4 percent aqueous solution of polyvinyl alcohol, said solution having a viscosity of 4 to 6 centipoises as measured by the Hoepp-ler falling ball method, and the amount of polyvinyl alcohol amounting to about 1 percent, by weight, of the mixture; placing the briquette in a controlled-gas furnace and raising the temperature to a sintering temperature of 2,350 degrees Fahrenheit degrees in air; maintaining the sintering temperature for six hours in an atmosphere or two parts of nitrogen to one part of air; and cooling the briquette in nitnogen without removal from the furnace.

-8. The method of making a magnetioferrite toroid core including the steps of pressing into a toroid briquette 0.0 055 gram of a pulverized mixture of Molar percent MgO 14.25 M 40.82 Fe O 41.23 ZnO 3.70

using as a binder a 4 percent aqueous solution of polyvinyl alcohol, said solution having a viscosity of 4 to 6 centipoises as measured by the Hoeppler falling ball method, and the amount of polyvinyl alcohol amounting to about 1 percent, by Weight, of the mixture; placing the briquette in a controlled-gas furnace and raising the temperature to a sintering temperature of 2,350 degrees Fahrenheit i100 degrees in air; maintaining the sintering ternperature for six hours in an atmosphere of one part of nitrogen to one part of air; and cooling the briquette in nitrogen without removal from the furnace.

References Cited in the file of this patent UNITED STATES PATENTS 2,640,813 Berge June 2, 1953 2,754,172 Went et a1 July 10, 1956 2,762,778 Gorter et a1 Sept. 11, 1956- 2,842,500 Gibson et a1. July 8, 1958 FOREIGN PATENTS 158,857 Australia May 29, 1952 167,499 Australia June 18, 1953 730,703 Great Britain May .25, 1955 OTHER REFERENCES Gorter: Proceedings of the IRE, Dec. 1955, pp. 1959, 1960.

Econom-os: J. Amer. Ceramic Soc., vol. 38, pp. 292 296, 356, 408411 (1955).

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent Now 3 109,817 November 5, 1963 Paul M. Miller It is hereby certified that error appears in the above numbered patent requiring correction and that the said Letters Patent should read as corrected below.

Column 1, lines 32 and 33, strike out such nitrogen addition increasing the coercivity of the end product" and insert the same after "air" in line 34, same column 1.

Signed and sealed this 28th day of April 1964,

(SEAL) Attest:

ERNEST W SWIDER EDWARD J,, BRENNER Attesting Officer Commissioner of Patents 

1. THE METHOD OF MAKING MAGNETIC-FERRITE MATERIAL INCLUDING THE STEPS OF MOLDING A BRIQUETTE OF A MIXTURE OF PULVERIZED MAGNESIUM OXIDE, MANGANESE OXIDE, IRON OXIDE, AND ZINC OXIDE WITHIN THE RANGES SHOWN IN THE DRAWING; HEATING THE BRIQUETTE IN A FURNACE, FIRST IN AIR TO 2,350 DEGREES FAHRENHEIT$100 DEGREES; CONTROLLING THE FURNACE TO MAINTAIN SAID TEMPERATURE FOR FROM THREE TO TEN HOURS AND DURING THIS TIME INTRODUCING A SELECTED AMOUNT OF NITROGEN INTO THE FURNACE TO REPLACE AN EQUIVALENT AMOUNT OF AIR ACCORDING TO INCREASED COERCIVITY DESIRED IN SAID MAGNETIC-FERRITE MATERIAL; AND COOLING THE SINTERED BRIQUETTE IN THE FURNACE IN NITROGEN. 